Sensor device, sensor module, force detection device, and robot

ABSTRACT

A package having a recessed section, a sensor element arranged in the recessed section and having a piezoelectric material, a lid joined to the package and sealing the recessed section of the package are provided. The package has a first hollow portion which a part of the sensor element fits with, on an inner bottom surface of the recessed section. The lid has a second hollow portion which a part of the sensor element fits with.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional patent application of U.S. application Ser. No.13/967,575 filed Aug. 15, 2013, which claims priority to Japanese PatentApplication No. 2012-182987 filed Aug. 22, 2012, both of which areincorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a sensor device, a sensor module, aforce detection device, and a robot.

2. Related Art

According to a related art, a force sensor disclosed in JP-A-4-231827 isknown as a force sensor using a piezoelectric material. JP-A-4-231827discloses a force sensor in which a signal electrode is held betweencrystal discs of a piezoelectric material and in which plural measuringelements held between metal cover discs are arranged inside a metal ringby welding.

FIG. 10 shows a sensor device according to a related art. As shown inFIG. 10, a sensor device 200 is formed as a whole by a metallic package202 having a sensor element 214 and a recessed section to accommodatethe sensor element 214, and a metallic plate-like lid 204 which isjoined to the top surface (joining surface 224) that is an outercircumference of an opening 220 of the recessed section of the package202 and which contacts the sensor element 214.

The sensor element 214 includes a detection electrode 218 insertedbetween two quartz plates 216 having the same cut surface, with thequartz plates 216 facing each other.

The top surface of the quartz plate 216 is a contact surface 222 of thesensor element 214 and contacts the lid 204.

Meanwhile, a coaxial connector 206 is attached to a lateral side of thepackage 202. The coaxial connector 206 has an outer circumferentialportion 208 and a center conductor 210. The space between these twocomponents is filled with an insulating resin 212, and the outercircumferential portion 208 and the center conductor 210 areelectrically insulated from each other. Here, the outer circumferentialportion 208 is short circuited with the package 202 and the lid 204, andthe center conductor 210 is electrically connected to the detectionelectrode 218.

This sensor device 200 is inserted between pressurizing plates (notshown) and thus pressurized. The lid 204 transmits a force (pressure) tothe contact surface 222 of the sensor element 214. Then, a force(pressure) applied to the quartz plates 216 changes according to anexternal force applied to the pressurizing plates. The quartz plates 216output (induce) electric charge accompanying this applied force, in thedetection electrode 218 by a piezoelectric effect. Therefore, byassuming a signal output in the case of pressurization only as areference output, and monitoring the amount of change in output electriccharge due to change in the force (pressure) via the coaxial connector206, the external force applied to the sensor device 200 can bedetected.

Here, in the sensor device 200, the sensor element 214 is sealed by thelid 204 in the state where the inside of the package 202 is filled withdry air so that the electric charge induced by the quartz plates 216does not leak because of a fall in insulation resistance due to moistureor the like.

The force sensor disclosed in JP-A-4-231827 has a structure in which asignal electrode is held between crystal discs and in which the crystaldiscs are held between metal cover discs. If this is welded to a metalring, the individual parts such as the signal electrode have dimensionaldifferences and the differences cause irregularities at the weldedportion, possibly generating a gap in the weld. Therefore, if theexternal environment is in poor condition such as high humidity, entryof moisture into the sensor element may cause leakage of electriccharge, making stable measurement difficult.

Meanwhile, in the related-art sensor device shown in FIG. 10, the heightof the contact surface 222 of the sensor element 214 accommodated in thepackage 202 and the height of the joining surface 224 that is the outercircumference of the opening 220 of the recessed section of the package202 may not coincide with each other in some cases.

FIGS. 11A to 11D show schematic views of the related-art sensor device(the height of the contact surface>the height of the joining surface).FIGS. 11A and 11B are plan and sectional views before the lid is joined.FIGS. 11C and 11D are plan and sectional views after the lid is joined.Here, for simplification, the quartz plates and detection electrode ascomponents of the sensor element 214, and the wire and connector fortaking out a signal outside the package are not shown.

As shown in FIGS. 11A and 11B, before the lid 204 is joined to thepackage 202, the sensor element 214 is aligned with and placed at thecenter of the recessed section of the package 202, and the lid 204 isplaced thereon to cover the opening 220 of the recessed section of thepackage 202. At this point, since there are manufacturing variances inthe heights of the package 202 and the sensor element 214, a gap 600 maybe formed between the lid 204 and the joining surface 224.

Next, as shown in FIG. 12, roller electrodes 280 are pressed againstpositions (joining surface 224) on the lid 204 that connect to thepackage 202, and a current is applied to the roller electrodes 280 tojoin and airtightly seal the lid 204 and the package 202 by seamwelding.

When this lid 204 is seam-welded, the sensor element 214 and the lid 204may be misaligned by vibrations in a carrying process or the pressingforce of the roller electrodes 280, and the lid 204 is often joined tothe package 202 with a misalignment as viewed in a plan view, as shownin FIG. 11C. In such a case, on the joining surface 224 between the lid204 and the package 202, a portion (insufficient joining area 270) wherethe lid 204 and the package 202 are joined together with only a veryshort length left between the inside and outside of the package isformed, as shown in FIG. 11D. This insufficient joining area 270 has lowstress resistance. Therefore, in the sensor device 200, to which a forceis applied repeatedly, repetition fatigue may break the joining betweenthe lid 204 and the package 202 and break the airtight sealing, thusimpairing reliability.

Meanwhile, if the contact surface between the package 202 and the sensorelement 214 and the contact surface between the sensor element 214 andthe lid 204 are bonded with an adhesive in order to prevent misalignmentof the sensor element 214 and the lid 204 at the time of seal welding, acreep phenomenon due to pressurization causes a long-term reduction inthe thickness of the adhesive layer, which causes a fall in appliedpressure. Thus, there is a problem that force detection characteristicsmay change or force detection may become impossible. Thus, in view ofthe characteristics and reliability of the sensor device, it is notpreferable to use an adhesive to bond the contact surface between thepackage 202 and the sensor element 214 and the contact surface betweenthe sensor element 214 and the lid 204.

SUMMARY

An advantage of some aspects of the invention is that a sensor device, asensor module, a force detection device, and a robot that can stablymaintain detection characteristics of a sensor element accommodated in apackage over a long period are provided by forming a stably produciblestructure of a package that does not easily deteriorate.

The invention can be implemented as the following application examples.

APPLICATION EXAMPLE 1

This application example is directed to a sensor device including: afirst member having a recessed section; a second member joined to thefirst member in such a way as to seal the recessed section; and a sensorelement having a piezoelectric material and arranged in the recessedsection. A first hollow portion which a part of the sensor element fitswith is formed on an inner bottom surface of the recessed section. Asecond hollow portion which a part of the sensor element fits with isformed on the second member.

According to this application example, the sensor element is alignedwith the first member in the state where the sensor element is fittedwith the first hollow portion, and the second member is aligned with thesensor element in the state where the sensor element is fitted with thesecond hollow portion. Therefore, the first member and the second memberare indirectly aligned with each other via the sensor element, and thefirst member and the second member are joined together without anymisalignment. Thus, the sensor device can be manufactured, stablysecuring a sufficient length between the inside and outside of thepackage on the joining surface between the first member and the secondmember. Therefore, the sensor device can stably maintain detectioncharacteristics of the sensor element accommodated in the first memberover a long period.

APPLICATION EXAMPLE 2

This application example is directed to the sensor device according tothe application example described above, wherein the sensor element hasa first contact surface which the first member contacts, and a secondcontact surface which the second member contacts, the first member has afirst flat portion having a flat surface which contacts the firstcontact surface, and the second member has a second flat portion havinga flat surface which contacts the second contact surface.

According to this application example, the first member and the sensorelement directly contact each other at the first flat portion and thefirst contact surface, and the second member and the sensor elementdirectly contact each other at the second flat portion and the secondcontact surface. There is no member that causes creep in thetransmission path of applied pressure. Therefore, a fall in appliedpressure due to a creep phenomenon does not occur. Thus the sensordevice can stably maintain detection characteristics of the sensorelement accommodated in the first member over a long period.

APPLICATION EXAMPLE 3

This application example is directed to the sensor device according tothe application example described above, wherein, if a normal directionof the second contact surface of the sensor element is a Z-axisdirection and directions orthogonal to the Z-axis direction andorthogonal to each other are X-axis direction and Y-axis direction, thesensor element has at least one of a first sensor element which detectsa force in the X-axis direction, a second sensor element which detects aforce in the Y-axis direction, and a third sensor element which detectsa force in the Z-axis direction.

According to this application example, a force in an arbitrary directioncan be detected according to purpose of use.

APPLICATION EXAMPLE 4

This application example is directed to a sensor module including: afirst member having a recessed section; a sensor element having apiezoelectric material and arranged in the recessed section; a secondmember joined to the first member in such a way as to seal the recessedsection; a first plate which contacts the first member; a second platewhich contacts the second member; and a fastening portion which fastensthe first plate and the second plate. The sensor element has a firstcontact surface which the first member contacts, and a second contactsurface which the second member contacts. A first hollow portion whichthe first contact surface fits with is formed on an inner bottom surfaceof the recessed section. A second hollow portion which the secondcontact surface fits with is formed on the second member.

According to this application example, for the same reasons asApplication Example 1, the sensor module can stably maintain detectioncharacteristics of the sensor element accommodated in the first memberover a long period.

APPLICATION EXAMPLE 5

This application example is directed to a force detection device has theabove sensor device.

According to this application example, for the same reasons asApplication Example 1, the force detection device can maintain detectioncharacteristics of the sensor element accommodated in the first memberover a long period.

APPLICATION EXAMPLE 6

This application example is directed to a force detection deviceincluding: a first member having a recessed section; a sensor elementhaving a piezoelectric material and arranged in the recessed section; asecond member joined to the first member in such a way as to seal therecessed section; and an electronic circuit which electrically connectsto the sensor element. The sensor element has a first contact surfacewhich the first member contacts, and a second contact surface which thesecond member contacts. A first hollow portion with which the firstcontact surface fits is formed on an inner bottom surface of therecessed section. A second hollow portion with which the second contactsurface fits is formed on the second member.

According to this application example, for the same reasons asApplication Example 1, the force detection device can maintain detectioncharacteristics of the sensor element accommodated in the first memberover a long period.

APPLICATION EXAMPLE 7

This application example is directed to a robot has the above forcedetection device.

According to this application example, for the same reasons asApplication Example 1, the robot can maintain detection characteristicsof the sensor element accommodated in the first member over a longperiod.

APPLICATION EXAMPLE 8

This application example is directed to a robot including: a main bodyportion; an arm portion connecting to the main body portion; and a handportion connecting to the arm portion. The robot has a sensor device ata connecting part between the arm portion and the hand portion. Thesensor device includes: a first member having a recessed section; asensor element having a piezoelectric material and arranged in therecessed section; and a second member joined to the first member in sucha way as to seal the recessed section. The sensor element has a firstcontact surface which the first member contacts, and a second contactsurface which the second member contacts. A first hollow portion whichthe first contact surface fits with is formed on an inner bottom surfaceof the recessed section. A second hollow portion which the secondcontact surface fits with is formed on the second member.

According to this application example, for the same reasons asApplication Example 1, the robot can maintain detection characteristicsof the sensor element accommodated in the first member over a longperiod and can detect an external force applied to the arm portion andthe hand portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like element.

FIGS. 1A and 1B are schematic views showing a sensor device according toa first embodiment. FIG. 1A is a plan view. FIG. 1B is a sectional viewtaken along A-A in FIG. 1A.

FIGS. 2A and 2B are sectional views showing modifications of a lid ofthe embodiment.

FIG. 3 is a sectional view showing a sensor device according to a secondembodiment.

FIG. 4 is a plan view showing the sensor device according to the secondembodiment (the lid is not shown).

FIG. 5 is a plan view showing a package base according to the secondembodiment.

FIG. 6 is a schematic view showing a sensor element according to thesecond embodiment.

FIG. 7 is a sectional view showing a sensor module according to a thirdembodiment.

FIG. 8 is a schematic view showing a force detection device according toa fourth embodiment.

FIG. 9 is a schematic view showing a robot equipped with a forcedetection device according to a fifth embodiment.

FIG. 10 is a schematic view showing a related-art sensor device.

FIGS. 11A to 11D are schematic views showing a related-art sensordevice. FIG. 11A is a plan view before the lid is joined to the package.FIG. 11B is a sectional view taken along B-B in FIG. 11A. FIG. 11C is aplan view after the lid is joined to the package. FIG. 11D is asectional view taken along C-C in FIG. 11C.

FIG. 12 is a schematic view showing the related-art sensor device at thetime of seam welding.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the invention will be described in detail, usingillustrated embodiments. However, components described in theembodiments, and kinds, combinations, shapes and relative positionsthereof are not intended to limit the scope of the invention to theembodiments but are simply illustrative examples unless otherwisestated.

First Embodiment

FIGS. 1A and 1B show schematic views of a sensor device according to afirst embodiment. FIG. 1A is a plan view. FIG. 1B is a sectional viewtaken along A-A in FIG. 1A. FIGS. 2A and 2B are sectional views showingmodifications of a lid of the embodiment. The basic configuration of asensor device 1 of the first embodiment is similar to the related-artsensor device 200. Therefore, the same components are denoted by thesame reference numerals and will not be described further in detailunless necessary.

The sensor device 1 of this embodiment is mainly formed by a package(first member) 202, a sensor element 214, and a lid (second member) 204.The package 202 has a recessed section. On the inner bottom surface ofthe recessed section, a first hollow portion 931 which a bottom part ofthe sensor element 214 fits with is formed. On the lid 204, a secondhollow portion 932 which a top part of the sensor element 214 fits withis formed.

The bottom part of the sensor element 214 is placed inside the firsthollow portion 931. The lid 204 is placed on the sensor element 214 inthe state where the second hollow portion 932 is fitted with the toppart of the sensor element 214, and the lid 204 covers an opening 220 ofthe recessed section of the package 202. The lid 204 is joined at itscircumferential edge to a joining surface 224 of the package 202. Thepackage 202 has a package structure with a recessed section and ismainly made of a metal, ceramics or the like. Although not shown, anelectrode, wire, connector or the like to take out output from thesensor element 214 outside of the package is properly provided on thepackage 202.

The lid 204 joined to the package 202 is made of a metal such asstainless steel or Kovar (or ceramics as will be described later). Thelid 204 may be shaped by pressing a flat thin plate to form the secondhollow portion 932 as shown in FIGS. 1A and 1B, or by shaving a plate toform the second hollow portion 932 to a thinner thickness than otherparts as shown in FIG. 2A, or by pressing a flat thin plate only at theperipheries of the second hollow portion 932.

The sensor device 1 of the embodiment is assembled as follows. First,the sensor element 214 is placed in the first hollow portion 931 insidethe recessed section of the package 202. Here, the flat portion of thefirst hollow portion 931 is formed, for example, to be 10 μm to 300 μmlarger than the outer dimension of the bottom surface of the sensorelement. Therefore, the bottom part of the sensor element can be easilyfitted with the flat portion and does not wobble. Next, the secondhollow portion 932 of the lid 204 is fitted with the top part of thesensor element 214. Here, the flat portion of the second hollow portion932 is formed, for example, to be 10 μm to 300 μm larger than the outerdimension of the top surface of the sensor element 214. Therefore, thesecond hollow portion 932 can be easily fitted with the top part of thesensor element 214 and does not wobble. Finally, in this state, seamwelding to join the package 202 and the lid 204 together is carried out.With such a configuration, the package 202 as the first member and thelid 204 as the second member are indirectly aligned with each other viathe sensor element 214 and do not wobble. Therefore, the sensor element214 and the lid 204 do not become misaligned by vibration in a carryingprocess of seam welding or the pressing force of roller electrodes.Thus, the sensor device can be produced, securing a sufficient lengthbetween the inside and outside of the package 202 at the circumferentialedge of the lid 204 and the joining surface 224 of the package 202.Therefore, the sensor device can stably maintain detectioncharacteristics of the sensor element 214 accommodated in the package202 over a long period.

The sensor device 1 of this embodiment is inserted, for example, betweenpressurizing plates 82 (FIG. 7), 92 (FIG. 8), described later, from anormal direction of a contact surface 222 of the sensor element 214 andis then pressurized. The bottom of the first hollow portion 931 of thepackage 202 is a flat surface (first flat portion 933) and is in surfacecontact with the bottom surface (first contact surface) of the sensorelement 214. The bottom of the second hollow portion 932 of the lid 204is a flat surface (second flat portion 934) and is in surface contactwith the top surface (second contact surface) of the sensor element 214.On these contact surfaces, direct contact takes place without using anadhesive or the like and there is no member that causes creep in thetransmission path of applied pressure. Therefore, a fall in appliedpressure due to a creep phenomenon does not occur. Thus, detectioncharacteristics of the sensor elements accommodated in the package canbe stably maintained for a long period.

Second Embodiment

FIG. 3 shows a sectional view of a sensor device according to a secondembodiment. FIG. 4 shows a plan view of the sensor device according tothe second embodiment (the lid is not shown). FIG. 5 shows a plan viewof a package base according to this embodiment. Here, FIG. 3 isequivalent to a sectional view taken along A-A in FIGS. 4 and 5. Asensor device 10 of the second embodiment, which is a device whichdetects forces in directions of orthogonal three axes, has the sameeffects and advantages as the sensor device 1 of the first embodiment.

The sensor device 10 of this embodiment is mainly formed by a package 12(first member), a sensor element 42, and a lid 34 (second member). Thepackage 12 has a recessed section. A first hollow portion 931 which abottom part of the sensor element 42 fits with is formed on the innerbottom surface of the recessed section. On the lid 34, a second hollowportion 932 which a top part of the sensor element 42 fits with isformed. The bottom part of the sensor element 42 is placed inside thefirst hollow portion 931. The lid 34 is placed on the sensor element 42in the state where the second hollow portion 932 is fitted with the toppart of the sensor element 42, and the lid 34 covers an opening 30 ofthe recessed section of the package 12. The lid 34 is joined at itscircumferential edge to a joining surface 32 of the package 12.

The sensor device 10 of this embodiment is then inserted betweenpressurizing plates 82 (FIG. 7), 92 (FIG. 8), described later, from anormal direction of a contact surface 44 of the sensor element 42 (fromthe γ-axis direction in FIG. 6) and is pressurized.

The package 12 is made of an insulating material such as ceramics. Thepackage 12 has a package base 14 which is in the shape of a rectangularflat plate (it may be disc-shaped or the like) as viewed in a plan viewfrom the direction of the depth of the recessed section of the package12 and on which the sensor element 42 is arranged. The package 12 alsohas a ring-shaped side wall member 24 having the same outer shape as thepackage base 14 as viewed in a plan view (FIG. 4) and arranged on thepackage base 14 in such a way as to surround the periphery of the sensorelement 42.

As shown in FIG. 5, a ground electrode 16 connecting to the sensorelement 42 is arranged at the center on the top surface of the packagebase 14. Side electrodes 20A, 20B, 20C, 20D are arranged at the (four)corner parts of the lateral sides of the package base 14. The sideelectrodes 20A, 20B, 20C, 20D are connected via a wire or the like, forexample, to an electronic circuit (not shown) which detects output fromthe sensor device 10.

As shown in FIGS. 3, 4 and 5, connection electrodes 18A, 18B, 18C, 18Dare arranged on the top surface of the package base 14. The connectionelectrodes 18A, 18B, 18C, 18D are arranged to be connected to the sideelectrodes 20A, 20B, 20C, 20D, respectively, and have one end thereofarranged at each corner position of the package base 14. The other endof the connection electrodes 18A, 18B, 18C is arranged near the groundelectrode 16. The other end of the connection electrode 18D is connectedto the ground electrode 16 via a through-electrode 29.

As shown in FIGS. 3 and 4, the side wall member 24 is stacked at aposition to be a circumferential edge on the package base 14. The sidewall member 24 is arranged to cover the connection electrodes 18A, 18B,18C, 18D. However, since the side wall member 24 is a rectangularring-shaped member, the side wall member 24 is stacked on the packagebase 14 in the state where the other end of the connection electrodes18A, 18B, 18C, 18D is exposed to the inner side of the side wall member24 and the ground electrode 16 is exposed as well. Thus, the side wallmember 24 forms the opening 30 of the recessed section of the package12.

As shown in FIG. 3, a metalized layer 26 is arranged on the top surfaceof the side wall member 24 and this becomes a joining surface 32 of thepackage 12 (side wall member 24). As shown in FIGS. 3 and 4, athrough-electrode 28 penetrating the side wall member 24 in thedirection of height is arranged at the position facing the connectionelectrode 18D, in the side wall member 24. The metalized layer 26 andthe connection electrode 18D are electrically connected to each othervia the through-electrode 28.

The ground electrode 16 and the connection electrodes 18A, 18B, 18C, 18Dare made of an electrically conductive metal. The metalized layer 26 canbe made of the same material as the ground electrode 16 and the like.

As shown in FIG. 3, the lid 34 is electrically connected to theconnection electrode 18D via the metalized layer 26 and thethrough-electrode 28. The process of joining the lid 34 of the sensordevice 10 of the second embodiment is similar to the first embodiment.

As shown in FIG. 3, the sensor element 42 is a plate-like substrate madeof, for example, quartz crystal, lead zirconate titanate (PZT:Pb(Zr,Ti)O₃), lithium niobate, lithium tantalate, having a piezoelectricproperty. In this embodiment, a quartz plate is used as a piezoelectricmaterial. The sensor element 42 includes a first sensor element 46, athird sensor element 58, and a second sensor element 52 stacked in orderfrom above. The first sensor element 46 includes first quartz plates48A, 48B formed to sandwich a first detection electrode 50. The secondsensor element 52 includes second quartz plates 54A, 54B formed tosandwich a second detection electrode 56. The third sensor element 58includes third quartz plates 60A, 60B to sandwich a third detectionelectrode 62.

A first ground electrode 64 is arranged between the first sensor element46 (first quartz plate 48B) and the third sensor element 58 (thirdquartz plate 60A). A second ground electrode 66 is arranged between thethird sensor element 58 (third quartz plate 60B) and the second sensorelement (second quartz plate 54A). The top surface of the first sensorelement 46 (first quartz plate 48A) is the contact surface 44 of thesensor element 42. This top surface contacts a force transmissionportion 36 of the lid 34 and is thus grounded. The bottom surface of thesecond sensor element 52 (second quartz plate 54B) is connected to theground electrode 16 and thus grounded.

As shown in FIG. 4, the first detection electrode 50, the seconddetection electrode 56, the third detection electrode 62, the firstground electrode 64, and the second ground electrode 66 are arranged,partly protruding from the first to third quartz plates. The firstdetection electrode 50 is connected to an exposed part (other end side)of the connection electrode 18A via an electrically conductive wire 68A.The second detection electrode 56 is connected to an exposed portion(other end side) of the connection electrode 18B via a wire 68B. Thethird detection electrode 62 is connected to an exposed portion (otherend side) of the connection electrode 18C via a wire 68C. The firstground electrode 64 and the second ground electrode 66 are connected toan exposed portion (other end side) of the connection electrode 18D viawires 68D, 68E, respectively.

By the above connection, the side electrode 20A is electricallyconnected to the first detection electrode 50 via the connectionelectrode 18A and the wire 68A. The side electrode 20B is electricallyconnected to the second detection electrode 56 via the connectionelectrode 18B and the wire 68B. The side electrode 20C is electricallyconnected to the third detection electrode 62 via the connectionelectrode 18C and the wire 68C.

The side electrode 20D is electrically connected to the ground electrode16 via the connection electrode 18 and the through-electrode 29.Moreover, the side electrode 20D is electrically connected to the firstground electrode 64 via the wire 68D connected to the connectionelectrode 18D. The side electrode 20D is also electrically connected tothe second ground electrode 66 via the wire 68E connected to theconnection electrode 18D. The side electrode 20D is also electricallyconnected to the lid 34 via the through-electrode 28 connected to theconnection electrode 18D and via the metalized layer 26.

As materials of the above various electrodes, gold, titanium, aluminum,copper, iron or the like may be used singly or in combination. Forexample, stainless steel can be used as an iron alloy and may preferablybe used because of its excellent durability and anti-corrosion.

FIG. 6 shows a schematic view of the sensor element of this embodiment.In this embodiment, the force transmission portion 36 can transmit notonly a force in a direction parallel to the normal direction (γ axis) ofthe contact surface 44 of the sensor element 42 but also forces in theplanar direction of the contact surface 44, that is, forces in twodirections (α axis, β axis) orthogonal to the γ axis and orthogonal toeach other, to the contact surface 44. The sensor element 42 (firstsensor element 46, second sensor element 52, third sensor element 58)can detect forces parallel to the α axis,β axis, and γ axis, asdescribed later.

In the first sensor element 46, the first quartz plates 48A, 48B aremade of Y-cut quartz plates and have such a crystal orientation that anX direction that is a crystal orientation to generate a piezoelectriceffect is perpendicular to the normal line (direction parallel to the γaxis in FIG. 6) of the first quartz plates 48A, 48B. The first quartzplates 48A, 48B are arranged in such a way that their respective Xdirections are opposite to each other. Moreover, the first quartz plates48A, 48B are arranged in such a way that their X directions are parallelto the α axis of the spatial orthogonal coordinate system.

In the second sensor element 52, the second quartz plates 54A, 54B aremade of Y-cut quartz plates and have such a crystal orientation that anX direction is perpendicular to the normal line (direction parallel tothe γ axis) of the second quartz plates 54A, 54B. The second quartzplates 54A, 54B are arranged in such a way that their respective Xdirections are opposite to each other. Moreover, the second quartzplates 54A, 54B are arranged in such a way that their X directions areparallel to the β axis of the spatial orthogonal coordinate system.

In the third sensor element 58, the third quartz plates 60A, 60B aremade of X-cut quartz plates and have such a crystal orientation that anX direction is parallel to the normal line (direction parallel to the γaxis) of the third quartz plates 60A, 60B. The third quartz plates 60A,60B are arranged in such a way that their respective X directions areopposite to each other. Moreover, the third quartz plates 60A, 60B arearranged in such a way that their X directions are parallel to the γaxis of the spatial orthogonal coordinate system.

As shown in FIG. 6, in the sensor element 42 of this embodiment, thedirection parallel to the γ axis of the spatial orthogonal coordinatesystem is the direction of height of the sensor device 10. As describedlater, the sensor element 42 is inserted between the pressurizing plates82 (FIG. 7), 92 (FIG. 8) from the direction of the γ axis, and thuspressurized by the pressurizing plates. Pressure is applied to thesensor element 42 from a direction parallel to the γ axis via the lid 34(force transmission portion 36). Thus, the third quartz plates 60A, 60Breceive applied pressure (compressive force) from the X direction andtherefore induce electric charge by a piezoelectric effect. The electriccharge (Fz signal) is outputted to the third detection electrode 62.

In the above configuration, if an external force that causes therelative positions of the two pressurizing plates to shift in adirection parallel to the α axis is applied, an external force parallelto the α axis is applied to the sensor element 42 via the forcetransmission portion 36. Then, the first quartz plates 48A, 48B receivean external force (shear force) from the X direction and thereforeelectric charge is induced by a piezoelectric effect. The electriccharge (Fx signal) is outputted to the first detection electrode 50.

Meanwhile, if an external force that causes the relative positions ofthe two pressurizing plates to shift in a direction parallel to the βaxis is applied, an external force parallel to the β axis is applied tothe sensor element 42 via the force transmission portion 36. Then, thesecond quartz plates 54A, 54B receive an external force (shear force)from the X direction and therefore electric charge is induced by apiezoelectric effect. The electric charge (Fy signal) is outputted tothe second detection electrode 56.

Moreover, if an external force that causes the relative positions of thetwo pressurizing plates to shift in a direction parallel to the γ axisis applied, an external force parallel to the γ axis is applied to thesensor element 42 via the force transmission portion 36. Then, the thirdquartz plates 60A, 60B receive an external force (compressive force ortensile force) from the X direction and therefore the amount of electriccharge induced by a piezoelectric effect changes. The amount of electriccharge (Fz signal) outputted to the third detection electrode 62changes.

Thus, the sensor device 10 of this embodiment can monitor the electriccharge (Fx signal) outputted to the first detection electrode 50 via theside electrode 20A, the electric charge (Fy signal) outputted to thesecond detection electrode 56 via the side electrode 20B, and theelectric charge (Fz signal) outputted to the third detection electrode62 via the side electrode 20C, and can detect the external forces (Fx,Fy, Fz) in the directions parallel to the α axis (X axis, as describedlater), theβ axis (Y axis, as described later), and the γ axis (Z axis,as described later), which are orthogonal to each other. While thesensor element 42 has a multilayer structure including the first sensorelement 46, the second sensor element 52, and the third sensor element58, the sensor element 42 may also have a configuration using at leastone or more. The first sensor element 46, the second sensor element 52,and the third sensor element 58 need not necessarily be stacked inlayers. Each sensor element may be accommodated in parallel inside thepackage 12 so that the force transmission portion 36 can contact the topsurface (contact surface) of each sensor element.

Third Embodiment

FIG. 7 shows a sectional view of a sensor module of this embodiment. Asensor module 80 of this embodiment has a configuration in which thesensor device 10 of the second embodiment (it may be the sensor device 1of the first embodiment) is inserted between the pressurizing plates 82and in which the pressurizing plates 82 are fastened to each other by afastening portion, thus pressurizing the sensor device 10.

The pressurizing plates 82 include a first plate 82 a which contacts thepackage 12, and a second plate 82 b which contacts the lid 34 (forcetransmission portion 36). The fastening portion includes a fasteningbolt 84 a and a fastening nut 84 b. In the first plate 82 a and thesecond plate 82 b, bolt holes 86 a through which the fastening bolt 84 ais inserted is formed and counterbores 86 b accommodating the head ofthe fastening bolt 84 a and the fastening nut 84 b are formed incommunication with the bolt holes 86 a.

Here, in the state where the sensor device 10 is held between the firstplate 82 a and the second plate 82 b, the fastening bolt 84 a isinserted through the bolt hole 86 a and the plates are fastened with thefastening bolt 84 a and the fastening nut 84 b. Then, the first plate 82a and the second plate 82 b receive forces in the direction ofapproaching each other from the fastening portion and the sensor device10 is pressurized in the direction of height. Thus, the lid 34 (forcetransmission portion 36) forming the sensor device 10 applies pressureto the contact surface 44 of the sensor element 42.

As in the foregoing embodiment, the side electrodes 20A, 20B, 20C, 20Dare connected to an electronic circuit (not shown) which receives asignal from the sensor device 10. Therefore, if an external force isapplied to the pressurizing plates 82, the external force is transmittedto the contact surface 44 via the force transmission portion 36 and theforce received by the contact surface 44 changes. This causes the outputof a signal outputted from the sensor device 10 to change. Thus, byusing the output of the signal in the case of pressurization only as areference and monitoring the amount of change in the output of thesignal, the force applied to the sensor module 80 (including thedirection of the force) can be detected. Also, an electronic circuit(not shown) may be embedded at the position on the first plate 82 a thatfaces the sensor device 10, and the side electrodes 20A, 20B, 20C, 20Dof the sensor device 10 maybe extended to the lower surface of thepackage 12. An electrode (not shown) mounted on the electronic circuit(not shown) and the portions of the side electrode 20A, 20B, 20C, 20Dextended to the lower surface of the package 12 may be soldered orconnected to each other by other measures.

Fourth Embodiment

FIG. 8 shows a force detection device of this embodiment. A forcedetection device 90 of this embodiment has a configuration in which foursensor devices 10 are held between two pressurizing plates 92. Anelectronic circuit (not shown) electrically connected to the sensordevices 10 via wires or the like is arranged. In the force detectiondevice 90, the four sensor devices 10 are inserted between thepressurizing plates 92 in the state where all the four sensor devices 10face the same direction, and pressure is then applied. For example, inthe sensor devices 10, the detection axis of the first sensor element 46(FIG. 6) faces a direction parallel to Fx. The detection axis of thesecond sensor element 52 (FIG. 6) faces a direction parallel to Fy. Thedetection axis of the third sensor element 58 (FIG. 6) faces a directionparallel to Fz.

Here, if a force that causes the relative positions of the pressurizingplates 92 to shift in the Fx direction is applied, the sensor devices 10detect forces Fxl, Fx2, Fx3, Fx4, respectively. If a force that causesthe relative positions of the pressurizing plates 92 to shift in the Fydirection is applied, the sensor devices 10 detect forces Fy1, Fy2, Fy3,Fy4, respectively. Moreover, if a force that causes the relativepositions of the pressurizing plates 92 to shift in the Fz direction isapplied, the sensor devices 10 detect forces Fzl, Fz2, Fz3, Fz4,respectively. Between the pressurizing plates 92, a relativedisplacement in which the pressurizing plates 92 shift from each otherin a direction of rotating about the X axis (Mx), a relativedisplacement in which the pressurizing plates 92 shift from each otherin a direction of rotating about the Y axis (My), and a relativedisplacement in which the pressurizing plates 92 shift from each otherin a direction of rotating about the Z axis (Mz) can take place. Forcesinvolved in these relative displacements can be transmitted to thesensor devices 10.

Therefore, in the force detection device 90, the forces Fx, Fy, Fzorthogonal to each other, the rotating force Mx about a directionparallel to Fx as its rotation axis, the rotating force My about adirection parallel to Fy as its rotation axis, and the rotation force Mzabout a direction parallel to Fz as its rotation axis can be calculatedas follows.

Fx=Fx1+Fx2+Fx3+Fx4

Fy=Fy1+Fy2+Fy3+Fy4

Fz=Fz1+Fz2+Fz3+Fz4

Mx=bX(Fz4=Fz2)

My=aX(Fz3-Fz1)

Mz=bX(Fx2-Fx4)+aX(Fy1-Fy3)

Here, a and b are constants. Therefore, the force detection device 90 ofthis embodiment can detect a force in any three-dimensional direction(forces in six-axis directions). The force detection device 90 canrealize airtight sealing of the sensor element 42 accommodated in thepackage 12 stably over a long period.

Fifth Embodiment

FIG. 9 shows a robot equipped with a force detection device according tothis embodiment. As shown in FIG. 9, a robot 100 includes a main bodyportion 102, an arm portion 104, a robot hand portion 116 or the like.The main body portion 102 is fixed, for example, onto a floor, wall,ceiling, movable trolley or the like. The arm portion 104 is providedmovably in relation to the main body portion 102. An actuator (notshown) which generates motive power to rotate the arm portion 104 and acontrol unit or the like (not shown) which controls the actuator areprovided inside the arm portion 104.

The arm portion 104 includes a first frame 106, a second frame 108, athird frame 110, a fourth frame 112, and a fifth frame 114. The firstframe 106 is connected to the main body portion 102 in such a way thatthe first frame 106 can rotate or bend in relation to the main bodyportion 102 via a rotating/bending axis. The second frame 108 isconnected to the first frame 106 and the third frame 110 viarotating/bending axes. The third frame 110 is connected to the secondframe 108 and the fourth frame 112 via rotating/bending axes. The fourthframe 112 is connected to the third frame 110 and the fifth frame 114via rotating/bending axes. The fifth frame 114 is connected to thefourth frame 112 via a rotating/bending axis. The arm portion 104 isdriven as each frame rotates or bends about each rotating/bending axisin combination with the other frames under the control of the controlunit.

The robot hand portion 116 is attached to the distal end of the fifthframe 114. A robot hand 120 that can grasp an object is connected to thefifth frame 114 via a robot hand connecting portion 118 having abuilt-in motor (not shown) which causes rotational operation.

Inside the robot hand connecting portion 118, the above force detectiondevice 90 (FIG. 8) is arranged in addition to the motor. Thus, when therobot hand portion 116 is moved to a predetermined operation positionunder the control of the control unit, the force detection device 90 candetect, as a force, contact with an obstacle or contact with an objectin response to an operation command beyond a predetermined position orthe like. The detected force can be fed back to the control unit of therobot 100 and an avoidance operation can be executed.

By using this robot 100, an obstacle avoidance operation, an objectdamage avoidance operation and the like which cannot be coped with bythe related-art position control can be easily carried out. The robot100 that can carry out safe and fine-tuned work can be provided.Moreover, the robot 100 can stably detect a force with high accuracyeven when the amount of displacement is small. The invention is notlimited to this embodiment and can also be applied to a two-arm robot.

What is claimed is:
 1. A sensor device comprising: a first member having a recessed section, a sensor element having a piezoelectric material and arranged in the recessed section, and a second member joined to the first member in such a way as to seal the recessed section, wherein the sensor element has: a first contact surface which the first member contacts, and a second contact surface which the second member contacts, a first hollow portion in which the first contact surface fits is formed on an inner bottom surface of the recessed section, and a second hollow portion in which the second contact surface fits is formed on the second member.
 2. The sensor device according to claim 1, wherein if a normal direction of the second contact surface of the sensor element is a Z-axis direction and directions orthogonal to the Z-axis direction and orthogonal to each other are X-axis direction and Y-axis direction, the sensor element has: at least one of a first sensor element which detects a force in the X-axis direction, a second sensor element which detects a force in the Y-axis direction, and a third sensor element which detects a force in the Z-axis direction, a sensor element having a piezoelectric material and arranged in the recessed section; a second member joined to the first member in such a way as to seal the recessed section; and an electronic circuit which electrically connects to the sensor element; wherein the sensor element has: a first contact surface which the first member contacts, and a second contact surface which the second member contacts, a first hollow portion which the first contact surface fits with is formed on an inner bottom surface of the recessed section, and a second hollow portion which the second contact surface fits with is formed on the second member. 